Solvent dewaxing



Oct- 6, 1953 w. KlERsTED, JR., r-:T AL 2,654,692

SOLVENT DEWAXING Filed April 7, 1950 UNITED STATES PATENT GFFICE S OLVEN T DEWAXIN G Wynkoop Kiersted, Jr., Scarsdale, and Howard H. Gross, Pleasantville, N. Y., assignors to Texaco Development Corporation, New York, N. Y., a corporation of Delaware Application April 7, 1950, Serial N o. 154,484 12 Claims. (Cl. 19618) ing wax cake, separating the slurry, and recycling vthe resulting filtrate to the dewaxing step. An essential element of this proposal involves carrying out the separation of the slurry at a tem- The present invention relates to solvent dewaxing of oil and more particularly, to the manufacturing of low pour-test lubricating oils from waxbearing mineral oils.

Broadly, the invention contemplates suppleinenting the product dewaxed mineral oil with 5 said that recycle of the resulting filtrate t0 the specific soft wax fractions sufficient in amount dewaxing operation results in an oil-free primary to increase materially the yield and quality of wax cake, all of the oil passing 01T in the dewaxed product without altering the pour point or apoil filtrate. By way of contrast, it is shown that preciably changing the cloud point. in the absence of such recycle, the wax cake con- Lubricating oils of low pour test, about 0 F., 10 tains 10-30% of oil. are produced from wax-bearing oils in the usual However, this process does not result in incorprocesses of solvent dewaxing by separating and poration of any appreciable portion of the reremoving crystallized wax from a chilled solventcycled vwax in the product oil filtrate. I-t accordoil-wax mixture. In accordance with the present ingly results in a progressive buildup of wax in invention, it has been discovered, however, that the System, necessitating periodic by-passing Of specific soft wax fractions contained in the wax the repulping operation, to disgorge the excess cake normally discarded and soluble in the deaccumulation of wax. waxing solvent at from 10 to 40 F. higher than The present invention, in sharp contrast to this the dewaxing temperature, but in no event above prior prOpOSal, provides a Continuously Operating F., are surprisingly compatible with the sep- 20 process free from wax buildup as the result of arated oil as regards pour test properties, and, in selective incorporation of the recycled soft wax addition to effecting a material increase in oi1 fraction in the primary filtrate. Therefore, the yield, impart other valuable properties to the product Oil, including that otherwise entrainedin final product oil. the primary wax cake, is additionally and sub- More speciiically, the invention involves incor- 25 stantially supplemented in accordance with the porating, in a low pour point cil, dewaxed at a amount of soft wax recycled and caused to pass temperature in the range from about 5 F; to into the primary ltrate.

F., a soft wax fraction of the primary de- In carrying out this invention, a wax-bearing waxing operation which dissolves in the dewaxhydrocarbon oil is miXed With a s01Vent and the ing solvent at temperatures about 10 to 40 F. 30 resulting mixture chilled to a dewaxing temperahigher than the dewaxing temperature, but never ture, in the range of from about 5 F. to 30 F. greater than a maximum of 25 F. Such soft wax to precipitate the solid hydrocarbons. For an oil fractions are compatible with the dewaxed prodof 0 F. pour point, the dewaxing temperature is uct oil from the primary dewaxing step, without abOut 15 F., and fOr a pour peint 0f 5 F'-, iS appreciable impairment of the low pour properusually about 10 F. ties. Therefore, direct mixture with the dewaxed The Cold mixture is iiltered to separate the oil product swells the yield by an amount equalto crystallized waxes and the resulting cake is the added fraction. washed with additional solvent in a primary lter, 0n the other hand, according to the preferred advantageously of the rotating drum type, which embodiment of the present invention, essentially produces a dewaxed filtrate and a filter cake of the same result is realized by cycling the soft wax wax, usually containing a small amount of enfraction to the charge to the primary dewaxing trained oil. I operation. Under such conditions, the major por- The primary iilter cake of wax is repulped 0I' tion of the recycled fraction tends to pass into mixed with a further quantity of dewaxing solthe filtrate to augment production, as above.` In vent and separated at a temperature in the other words, it has been found that, following crtical range from about 10 to 40 F'. above the this procedure, a substantial portion of the detemperature of the primary dewaxing operationsired soft wax fraction appears in theY primary As above indicated, if primary dewaxing is dewaxed oil stream. y carried out above 15 F., then the separation 'Recycle of the soft wax fractions in this man- Of the replllped WaX cake must be lower than ner is advantageous in that it appears to eect the upper limit 0f the 10 t0 40 F. range of inan improved fractionation of the waxes so that crease, because otherwise the retreatment temthe resulting oii contains only the desired porperature would exceed the critical upper limit tions of the soft wax. As a result, the yield Vof 0f 25 F. At temperatures above 25 F., the wax product oil tends to be augmented exclusively fraction Which passes 01T with the repulping solwith that portion of the soft wax fractions devent is no longer compatible with the primary sirable in accordance with the present invention. ltlate and therefore. instead 0f passing into It has been proposed to overcome the loss of the primary filtrate, builds up in the primary product oil whichtends to remain absorbed, by dewaxing OperatiOnocclusion orentrainment in the wax cake,.by the Therefele, at a temperature from 10 t0 40 F. steps of repulping or reslurrying the voil-containabove that 0f primary dewaxing, but not greater perature in the critical range of 30-35 F. It isv than 25"` F., the. repulpedwax, together with any small quantity of occluded oil is subjected to a secondary ltraticn, yielding a nal filter cake f hard wax and a filtrate containing lrelativelyeu soft wax fractions soluble therein at the yseconde ary filtration temperature, tegetherwithlessen,-d

tially all the occluded oil.

Instead of simple repulping of the primary wax;

cake, it may be recrystallized by dissolving in the added solvent perature, followed by a chilling to the range about to 40 F. above the primary de waxing temperature but not greater than F., as above, and then subjecting the chilled mixture tojsecondary filtration, In: other words, recovery or alrsecondary filtrate containing the desired soft wage fraction is dependent on the temperature at which the secondary filtrationV operation is carried out, as aL result ot the solubility of the waarin the solvent at thatteiriperature.l There-` fore," similar broad general results are realized whether the recovery of the soft wax fraction is efected by recrystallization or simple. repulping of the wax cake. Repulping, however, is adlanf. tageous inv that a more effective; separation is usually obtainable between thehard and the soft warg ractionsi Aslabovejintim ated, the secondary filtrate containing theV desired soft wax fractions is preferablypassed, continuously as a recycle streaml to the primary dewaxing operation. The resulting primary filtrate is continuously subjected to treatment for the recovery of the dewaxed oil, as above.. The dewaxed oil product yield is increased by an amount comparable to the amount or; soft waxiraction returned from the secondaly filtration, in addition to any recovered oil whichA may have been occluded in the wax cake.

Thus,l in a typical operation, the present invention results in a yield increase of, for example, 11/2 to 2 or 3 percent over the amountvof desired low, pour-test product otherwise recoverable withoutimpairment of the desired properties.. 'Illiat1 istos'ay, the poury test remains the same as that of oil, fromI the primary dewaxing with- 'outu recycle or soft wax fractions.

additional important advantage,l however,

'residesiii'the fact, that the components. incorporated in the product oil by practice of the present invention are beneficial from the standpoint` of stability andv l bricating1 properties. For example, the oilgcontainingadded soft waxwfraction in Yaccerdance.withthe present inventionis substantially more. stable thanV oil produced, by simple dewaxingn under the Same conditiorlSv without return of the repulped iltrate. ASA-a result, thereuuirementi fors Stabiliaine.Y additive necessary to meet exacting lubricating oilA stability requirements. i'ssubstantially decreased.- Thesolvent usedincarrying out the-.process is preferably ofV thel selective type. By selective solvent isr meant a solvent havingY a substantially complete solvent action upon the liquid hydrocarbon constituents ofthe oil at such terriperaf tures. A mixture of* aliphatic ketone, such as acetone, methyl ethyl ketone or methyl isobutyl ketone, and an aromatic hydrocarbon, such as benzol, or amixture of benzol and toluol, may serve as solvent. Methylene chloride, per, s e is also suitable.

Where a diluent type of solvent is employed, it may be a petroleum naphtha,naturalgasoline or a mixture of light hydrocarbons, suchV as, is derived from natural gasoline. Y y

at a suitably. elevated @6111-,

"which is precipitated from etudes suchv as I BihQlSSSat.

'-Ilie invention is particularly adanted to the dewaxing of wax-bearing oil containing Wax therefrom in relatively pure form.V Examples of such oils are distillates substantially tree from naturally occurring wax crystal modifying substances which are derived Pennsylvania, East Texas, parainpus Venezuelan, etc. Such dstillateslcontain, to 50% of wax by volume of theoil, n

` The temperature range of secondary dewaxing egim-,ration is critical from the standpoint that temperatures above thefeiective range result in a filtrate. lontainingl undesirable wax, fractions which adversely. affect thepour test propertiesl ot a. dewaxed. Voili 'Thereiore inclusion. ci these undesirable wax fractions inl the nalA even small amounts adversely afleots its pour test. Even when, reeycled to the, primary dewaxing operation, such fractions similarly tend to impair the oil product, and in addition, to build up. inthe system, overloading and adversely affect.- ing the separatlDn.,

Unless4 the secondary dewaxing operation is carried out4 at least about 10 F. above the primary dewaxing temperature, there is no apbrer. ciablepassage of the recyoledwax fraction into. the nrmaryot. and, there is no determinableim.- movement in product oil. duality., Y

rIfo Vfurther illustrate the operation, of' the. inf vention, referenceV willv now be made to, the accompanvine drawing, showing a flow diagram oi. the presentfprocess,

L WaX-loearlile` Pennsylvania oil having. a` Say.-l bolt universal viscosity ol, about 45 seconds. at 2 1 0' E. andcont-aining about 12% wax by volume, islDtrQduQed. from asciuroe not shown through a pipe l0 leading to a chiller I2. Into the Qil @barge is introduced.. from. ripe 13.', a. stream. of secondaryV filtrate Whidlflswll be, hereinafter de.- scribed.

A solvent liquid Vconsisting of a mixture of llllQllll'A 40% methyl ethyl ltetolleI and 60% benzol is. recycled, from a recovery source, also to be. iurther descubed.;y andipasses through. pipe. lili into the oil charge.A `The oil and' solvent. are mixed' in. the. pportlon of` about. one part oi oil to about three parts ofgsolventpervclume.

The. .roultnemxture passes, toA thel chlller.` l2 Where. it ishchilledto: a low temperature, as for examulerl'ain orderto precipitatetriesolid v Frornjthe chillerhthe coldKmixture passest'oa eelianlg l5... frorawliioh it. is. conducted toparrimary; filter lit; wherein the. solid; hrdrof cartons. are removed-as. a alternare of wax, nro.- duone, a primary dewaxed. nitrate drawn, on throughpipe |'3"i ntp .primary filtrate receiver IB; The resultingpfilter cake is washed, in situ, with i-rjeslrsolvent` .introduced via pipe, 21,v using, for example, about' .015 t. 1:0 .volume or; soi'iierittc one volume of'oilf'charge. The resulting filter cake, @mailling SmalL quantities oil adhering oil.L and solvent Ynot removedby. the washing step., is, dis: charged into receiving and'repulping section 22. ofthe primary lter in whichv it is repulnedwith an additional stream ofjsolvent fromA branch` pipe 24.

.f'hegleplllpllg. .SQiliLent pipe-2 4. is advantaeeouslr. at ,a temperaturfeof around 4 5?- r'. as. a resultpoipassage throughV heat A,exchanger 25' and le;t addedgin .sum ient .proportions such.. tharthe fina repulpedjwaxf'solvent" mixture` temperature illel .aboutT -illj At, thatemperav 5 ture, the repulped wax cake moves through pipe 21 into secondary feed tank 28. Trim chillers or exchangers, not shown, may be employed where necessary to maintain the desired exemplary temperature of 15 F. in the feed tanks and filters. At this temperature, the mixture is fed to a secondary filter 30 to form a secondary hard wax cake and a secondary filtrate.

The secondary wax cake also is washed in situ with solvent from branch pipe 32, at a temperature controlled by exchanger 33 until it is substantially free from oil. The wash solvent may be employed in theA proportion of about 1% part of solvent to one part of original oil charged to the primary operation.

The secondary filtrate, which comprises, in part, wash filtrate, is drawn off through pipe 35 into secondary ltrate receiver 36, and from there, conducted all or in part through the aforementioned pipe I3 into the primary dewaxing stage where it is mixed with the wax-bearing oil and solvent, and introduced into the primary filter I1.

The primary ltrate in the receiver I3 passes through pipe 38 to a dewaxed oil recovery system 39, discharging the iinal dewaxed product oil as at 40. The solvent recovered in this operation discharges into aforementioned pipe I4 for recycle to the system. To this end, branch pipe 42 connects with the aforementioned Washing and repulping solvent lines 2|, 24 and 32, respectively.

The secondary wax cake is conducted similarly to a hard wax recovery system 43, discharging the final hard waxes at 44 and returning the separated solvent through pipe 45 into the solvent recycle line 42.

The secondary filtrate in receiver 36 is at a temperature around 15 F. and is mixed with the oil charge in the Chiller I2 to maintain in the primary dewaxing step the temperature of about -16'F., which is that desired in order to produce a dewaxed oil having a pour test of about F. and below.

Following is a table comparing the pour point and cloud point of the product dewaxed oil of the foregoing process A t0 that of an identical oil subjected to the same primary dewaxing treatment but without recycle of soft wax fractions from the primary wax cake B:

Pour Cloud Point, Point, F. F.

A o +5 B o +4 In addition, the operation results in a regular overall yield of product oil about 2% greater than that realized by simple primary dewaxing with recovery of any oil occluded in the primary wax cake.

Moreover, the amount of additive required to meet the same dewaxed oil stability specifications is only about half that required to stabilize the dewaxed oil from the primary filtrate when the repulped filtrate is not returned to the primary operation.

By way of explaining theoretically the passage of the recycled soft wax fraction into the primary filtrate, it is believed that this fraction is actually soluble, per se, in the primary dewaxing solvent at the separation temperature, but, nevertheless, is ordinarily caused to precipitatel by association with the predominant, relatively hard wax crystals. The recycled soft wax, however, appears to raise the concentration of this fraction in the primary separator to a level greater than that which is precipitated by association with the crystallized hard wax. Therefore, the soft wax tends to remain in solution in the oil and pass off with the primary filtrate.

The dotted line portion of the flow diagram represents a modified alternative procedure wherein the soft wax fraction or ony portion thereof is mixed directly with the dewaxed oil from the primary dewaxing operation. It contemplates diverting the secondary filtrate from line I3 into dotted line45, through which the filtrate is introduced into a soft wax recovery sectionv 46. Recovered solvent may be returned through line 41 into solvent return pipe 42. All, or any desired portion of the soft wax, preferably slurr'ied in a small amount of accompanying oil, passes through pipe 50 directly into the dewaxed oil, being recovered through line 40. The soft wax slurry exhibits complete solubility in this oil and yields arir oil mixture having essentially the desired low pour-test properties of the oil prior to admixture. Any portion of the soft wax not introduced into the dewaxed oil is discharged from the system through line 49.

Advantageously, recycle of the rep-ulp filtrate to the primary dewaxing operation may be cornbined with the steps of soft wax recovery and incorporation in the product oil exemplified by the dotted line portion of the flow sheet. For example, a portion of the filtrate in line I3 may be withdrawn through line 45 for treatment, as above, while the remainder is recycled to primary dewaxing,

The operations may be variously modified, if desired. For example, it is possible, and it is frequently desirable, to recycle primary filtrate from the receiver I9 to the inlet of the primary filter in order to procure a liquid-solids ratio favorable for optimum filtration. Moreover, it is contemplated employing heat exchangers, where effective to realize maximum thermal efliciency; for example, it is advantageous indirectly to heat exchange the chilled primary filtrate at, for instance, -15 F., with the incoming oil charge in advance of chiller I2. As a further modification, it is advantageous to inject the solvent into the oil charge in incremental additions, preferably during the course of the chilling operation.

Moreover, as previously indicated, the repulping of the primary wax cake may take place at any desired temperature, followed by later chilling or other temperature adjustment to. the range of secondary dewaxing.

Reference has been made to the dewaxing solvent mixture of methyl ethyl ketone, benzol and toluol. Also contemplated are mixtures of ke'- tones and other aliphatic compounds, as well as other solvents composed of a wax antisolvent and an oil solvent.

It is contemplated that the solvent ratios, as set forth in the specific example above, may vary widely, in accordance with known practice, depending upon the nature and source of the waxbearing oil undergoing treatment and the solvent employed.

Obviously, manyy modifications and variations of the invention, as above set forth, may be made without departing from the spirit and scope thereof, yand therefore, only such limitations should be imposed as are indicatedvin theap-v pended claims.`

i We claim:

1f. In the production of a low pour-test hydrocarbon oil from wax-bearing stock involving devvaxing said stock from a cold solution thereof in a dewaxing solvent, by steps comprising mixing the oi-l with a solvent. having substantially complete solvent action upon the liquid hydrocarbon constituents of the stock atv dewaxi'ng temperature, chilling the mixture to a dewaxing temperature. to crystallize waxes, and filtering the cold mixture in a filtration stage to produce a ltrate containing a product oil and a'primary lter cake of' wax substantially free from oil,l the improvement which comprises separating from said primary lter cake a soft. wax fraction by repulping said wax cake in said solvent at a temperature within the range from about lA to 40 F. above said dewaxin-g temperature, but'not any event at a temperature greater than 25 E., and c-:omlbiningv separated soft wax fraction with the dewaxed oit to yield an increased quantity of product oil of. unaltered: pour properties.

The method according to:- claim l, whereinthe primary deWaXi-ng step is eiiected at a ternperaturein the.- range ofabout 5 F.. to about 30 F.

3. In the production of. a low pour-test hydrocarbon oil from wax-bearing stock involving dewax-ng said stock from.= a coldsolution thereof in a; dewaxing solventby steps comprising mixing thev oil with a solvent, chilling the mixture-to a devvaxing temperature-to crys-tallize waxes, andl ltering, the cold mixture to produce a .primary dewaxed producty oilfiltrate and a primary Wax filterI cake, the improvement which comprises' treating. said primary' Wax lter cake` with addi-t ltional said solvent at a temperature within. the range of from about 1.0 to 40 F. higher than said dew-axingf temperature: but.. not any event greater than a tempera-ture; of 25-""F'., to separate. therefrom an extract soft. wax'. fraction', andz con.- tinuously introducing separated; soft Waxy fraction-` .as a feed. to.l said'. primary' dewaxing' opera:- tion thereby causingr said. soft wax' fraction' to' pass into the primary filtrate to substantially' augment the. quantity-'of' productoil without. de;- tracting from'itspourfproperties.

4. The-method. accordingv to claim 3i wherein'1 theprimaryrdervaxingstep is effected atLa: temperature in'. the; range of.' about. 5 E.' tabout -30.' F.'

5. In.'V the, production of a. low pour-test hydro.-.- carbon-.oil from;wax;bearing. stock: involving dewaxing said` stock'. from acold solution thereof; ini a. dewaxing' solvent, by. stepsi comprising ing the oilwith' asolvenu.chilling'tliamixture4 to a dewaxing temperature to crystallizewaxes; andv filtering the cold: mixture: to'. produce a primaryA dewaxed product oil. filtrate: anda' primaryf lter cakeof wax, the.4 improvement whichcom-` prises separating. a; mixture` of' primary' lter cake with additional said; solvent-at. a tempera-r ture in the range from to 40 F. higher than'-` said.dewaxingtemperatura but' not; inany event, greater than a temperature of? to' yield.l ai nitrate containing. a soft Wax. fraction.V soluble therein at said: separationtemperature; and con-L tinuouslyr supplying: separated'. softi Wax-1fraction'l as a feed to said dewaxing operation'l thereby: causingf saidfL soft; wax. fraction. to. pass into the primary' iiltrateto substantially.- augment'V the quantity of primaryproduct oilwvithout detract-f ing .from its pour properties-.

V6. The method`l accordingl to' claima;i wherein.v the primary dewaxing step is effected'fat abtemf' perature in the range or about 5 F. to about 30 E'. Y

7. In the production of a low pour-test hydrocarbon. oil from wax-bearing stock involving dw-axing said stock from a cold solution thereof in a dewaxing solvent of the selective type, by steps' comprising mixing the o-il with the solvent, chilling the mixture to a dewaxing. temperature to crystallize waxes and filtering the cold mixture to produce a deWaXed product oil filtrate and a primary lter cake of wax, the ir'nprovmenf. which comprises reptil-ping said l-te'r cake with additional said solvent at a temperature r'i the' range from 10 to 40 F. higher than said d'ewaxing temperature, but not in any event greater? than a temperaturel of 25 F., separating f'ron the repulped. mixtureV solvent contain-ing' soft' vv'ax fractions of the ilt'er cake l'terable therewith atv said repuIpi-'ng temperatura. and supplying separated soft wax fractions as a feed to said dewaxing operation thereby causing said soft wax fraction to pass into the primary l'trate to substantially augment the quantity ofY dewaxed product oil withouty detracting from its pour f properties.

y 8. The method according to claim 7, wherein the primary dewaxingfstep is effected at a ternperature in the range of about 5 F. to about 30 FL.

9. In. the production of a low peur-test hydrocarbon oil from Wax-bearingy stock involving dewaxing said stock from a coldI solution thereof in a dewaxing solvent of the selective type having substantially complete solvent action upon the liquid hydrocarbon constituents of` thestock' at dewaxi'ng temperaturaby steps comprising. mixing the oilv with the solvent; chilling the. mixture to aA dewaxing temperature to crystallize waxes. and' nltering they cold mixture ltoprodu a dewaxed! producty oil filtrate from which dewaxed product oil' is recovered,l and a filter cake ofI wax substantially free from oil4, the improvement' which comprises repulping. said lter cake with additional' said solvent at a 'temperature in the range from loto 40 F...higher thanv said dewaxing temperature, but not in any. event greater than a temperatureof 25 F2, separatingfrom the repulped mixture a nitrate. contaming soft wax fractions of the. lter cake. lili'lerabl'eA therewith at said repulping temperature, and combining thus separated soft wax fractions with the dewaxed product oil'to substantially augment the'quantity' ory product oil without detracting from its pour properties.V

1 0..V The method according to claim 9, wherein the primary dewaxing step is effected at a tempegture-in the. range ofA about 5 to about f Y ll. The method according to claiml wherein said wax'bearing stock ijs'sub'stantiallyifrefrom naturally' occurring' Wax' crystal modifying` sub'- stances. y Y

12. The method according to claimw 3 wherein said wax bearing. stock is substantially free from naturally' occurring wax" crystal modifying substances.'

WYNKO'OPKIERSTED, Ji'i'. HOWARD'HL GROSS'.y

References Cited in the file of thS-p'atenti'- UNITED STATESPATENTS Number vName a Datei 262,252,659 Y l a-.. Jam. 28, 194iasfisgisa d Y A May4 9.1.1944:`l 72,463,845' Baclslundet al. sans. Mar. 8,;5194911 

1. IN THE PRODUCTION OF A LOW POUR-TEST HYDROCARBON OIL FROM WAX-BEARING STOCK INVOLVING DEWAXING SAID STOCK FROM A COLD SOLUTION THEREOF IN A DEWAXING SOLVENT, BY STEPS COMPRISING MIXING THE OIL WITH A SOLVENT HAVING SUBSTANTIALLY COMPLETE SOLVENT ACTION UPON THE LIQUID HYDROCARBON CONSTITUENTS OF THE STOCK AT DEWAXING TEMPERATURE, CHILLING THE MIXTURE TO A DEWAXING TEMPERATURE TO CRYSTALLIZE WAXES,AND FILTERING THE COLD MIXTURE IN A FILTERATION STAGE TO PRODUCE A FILTRATE CONTAINING A PRODUCT OIL AND A PRIMARY FILTER CAKE OF WAX SUBSTANTIALLY FREE FROM OIL, THE IMPROVEMENT WHICH COMPRISES SEPARATING FROM SAID PRIMARY FILTER CAKE A SOFT WAX FRACTION BY REPULPING SAID WAX CAKE IN SAID SOLVENT AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT 10 TO 40* F. ABOVE SAID DEWAXING TEMPERATURE,BUT NOT IN ANY EVENT AT A TEMPERATURE GREATER THAN 25* F., AND COMBINING SEPARATED SOFT WAX FRACTION WITH THE DEWAXED OIL TO YIELD AN INCREASED QUANTITY OF PRODUCT OIL OF UNALTERED POUR PROPERTIES.
 3. IN THE PRODUCTION OF A LOW POUR-TEST HYDROCARBON OIL FROM WAX-BEARING STOCK INVOLVING DEWAXING SAID STOCK FROM A COLD SOLUTION THEREOF IN A DEWAXING SOLVENT, BY STEPS COMPRISING MIXING THE OIL WITH A SOLVENT, CHILLING THE MIXTURE TO A DEWAXING TEMPERATURE TO CRYSTALLIZE WAXES, AND FILTERING THE COLD MIXTURE TO PRODUCE A PRIMARY DEWAXED PRODUCT OIL FILTRATE AND A PRIMARY WAX FILTER CAKE, THE IMPROVEMENT WHICH COMPRISES TREATING SAID PRIMARY WAX FILTER CAKE WITH ADDITIONAL SAID SOLVENT AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 10 TO 40* F. HIGHER THAN SAID DEWAXING TEMPERATURE BUT NOT IN ANY EVENT GREATER THAN A TEMPERATURE OF 25* F., TO SEPARATE THEREFROM AN EXTRACT SOFT WAX FRACTION, AND CONTINUOUSLY INTRODUCING SEPARATED SOFT WAX FRACTION AS A FEED TO SAID PRIMARY DEWAXING OPERATION THEREBY CAUSING SAID SOFT WAX FRACTION TO PASS INTO THE PRIMARY FILTRATE TO SUBSTANTIALLY AUGMENT THE QUANTITY OF PRODUCT OIL WITHOUT DETRACTING FROM ITS POUR PROPERTIES. 